1. Department of Physics and Energy Sciences, University of Colorado at Colorado Springs, 1420 Austin Bluffs Pkwy, Colorado Springs, Colorado 80933, USA
2. Argonne National Laboratory, Center for Nanoscale Materials, Argonne, Illinois 60439, USA
3. Chernivtsi National University, 2 Kotsiubynskogo Str., Chernivtsi 58012, Ukraine